The market for such tools has been strong in countries that heavily use payment cards, so it's probably not surprising that the trade would rise in China.

But it does mean that retailers there may begin face to facing an increasing risk from data breaches that have stung companies such as Target, Home Depot and many others.

One website found by Gu offered point-of-sale devices that had been modified in order to send payment card details captured from a card's magnetic stripe over SMS to fraudsters.

The way the devices are sold -- from the criminals to resellers to retailers and then onto businesses -- means some in the supply chain may not know the devices have been altered. It's also advantageous for the cybercriminals, Gu wrote.

"Cybercriminals do not even have to physically collect stolen information from installed devices, allowing them greater flexibility and convenience," he wrote.

ATM skimmers are also sold on some business-to-business online marketplaces for around ¥4,000 (US$630). These are usually devices that fit over an ATM's card slot and can record card details. Gu wrote some come with PIN pad overlays, which record a card's secret number.

Another product Gu found is aimed at people who have brief access to a person's payment card, a so-called "pocket skimmer"

"An unscrupulous store staff member can, for instance, swipe an unwitting customer’s card on a pocket skimmer in order to steal track data that he/she can later use for fraud," he wrote.

The pocket skimmer doesn't need a network connection or an external power supply. It can collect the details of up to 2,048 cards, which can be downloaded to a computer later with a USB cable.

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